This invention relates generally to the field of locks, and more specifically to deadbolt locks for use in a door.
1. Field of the Invention
An essential feature of any lock mechanism is to provide the requisite degree of security to the particular closure member in which the mechanism is to be used. In particular, deadbolt lock mechanisms are often used when the maximum degree of security is desired, such as, for example to prevent unauthorized access to a building through a locked door.
The degree of security offered by a deadbolt lock is a function of two interrelated parameters, namely bolt throw and structural displacement. Bolt throw is the distance that the lock bolt extends from the surface in which it is mounted into an adjacent structure, typically a door jamb or threshold. Structural displacement refers to the size of the opening that needs to be provided in the door to accomodate the lock mechanism, and is directly related to the overall size of the lock housing or casing. These two parameters are in inverse relationship to each other in that the maximum degree of security is obtained when bolt throw is at a maximum while structural displacement is at a minimum. The reasons for the inverse relationship are due to the fact that as bolt throw increases, the degree of security increases in that it becomes increasingly difficult to "spring" or "jimmy" a door open due to the length of the lock bolt disposed within the adjacent structure. Conversely, as the dimensions of a lock housing increase, a correspondingly large opening must be provided in the door to accomodate the lock housing; that is, the structural displacement increases. As the structural displacement increases, larger portions of the door are removed with a resulting decrease in the structural integrity of the door, thus making the door more susceptible to breakage by force and thereby decreasing the degree of security.
From the foregoing, it can be seen that the primary objectives in the art of deadbolt lock mechanisms is to achieve maximum security by maximizing bolt throw while minimizing the overall dimensions of the lock mechanism. Stated simply, it is a primary objective to reduce the size of the lock housing and then take full advantage of the dimension of the housing to achieve a maximum bolt throw.
2. Prior Art
In an effort to achieve the above-described objectives, numerous lock mechanisms have been developed and patented. Initially, these known devices, such as those disclosed in U.S. Pat. Nos. 3,026,703 and 3,011,817, provided a lock mechanism in which the bolt was actuated directly by use of a locking tab attached to the lock cylinder. In these devices, as the locking tab is rotated, it contacts a spring-loaded plunger detent which is then moved, against the force of the spring and in a direction transverse to the direction of the bolt movement, to a position whereby the bolt can be slid into its locked or unlocked position. Further rotation of the locking tab engages the tab with the bolt and the bolt is then pushed into position by the tab, at which time the plunger detent is moved in the opposite direction by the force of the spring to deadlock the bolt. These locks suffer the disadvantage in that the amount of bolt throw that can be achieved is limited to the portion of the arcuate motion of the tab that can be utilized to push the bolt into position. A further disadvantage of these known lock mechanisms is that they often require a number of moving parts in complex relationship and are thus costly and time consuming to manufacture and assemble. Still another disadvantage of these locks is that they often require modification of the locking tab, which also adds an additional cost to manufacture of the lock.
Other lock mechanisms are known, such as those disclosed in U.S. Pat. Nos. 2,854,839, 2,989,859, 3,899,906 and 4,218,903, which utilize a lever and swinging pivot bolt arrangement to increase the bolt throw. These mechanisms also utilize a spring-urged latching detent to deadlock the bolt in position and thus suffer from the same manufacture and assembly disadvantages noted above. Furthermore, in order to accommodate the lever and the swinging bolt, the size of the housing or casing of these locks and thus the structural displacement of the door, is undesirably large. Moreover, because the swinging bolt pivots into a locked or unlocked position, the bolt-receiving opening in the door jamb or threshold must be large enough to accomodate the arcuate path of the bolt, thus resulting in a large structural displacement within the receiving surface, which is also undesirable.